This project examines the interaction of genetic and environmental factors as they relate to antisocial behavior. The initial goal of the project is to determine whether any genetic factors relate to antisocial behavior. This is being investigated by means of the twin and adoption methods. In twin research we examine whether the concordance rates for registered antisocial behavior differ for mono- and dizygotic twins. In the adoption research we are studying individuals who were adopted at or near birth. They have had almost no postnatal contact with their biological parents. We are attempting to see whether the criminality in these adoptees is related to criminality in their biological parents. This would suggest some genetic contribution to the etiology of antisoical behavior. If such an etiology can be established then it would strongly suggest that biological factors are in some way involved among the causes of crime. A less obvious consequence is that we will be able to use these populations to examine environmental factors relating to criminality since we will be able to partially control the genetic variance. We will also be in a position to examine how the genetic and environmental variables interact. These interactions will be studied for the different types of crimes (e.g., property, violent, or sexual offenses). A distinctive feature of this work will be the sheer size and completeness of the populations being investigated. In the case of the adoptees we are stuyding 14,342 adoptions. In each case this means we are examining the adoptees, both biological and both adoptive parents. In the case of the twins we will be studying the total population of twins born between 1891 and 1920 in Denmark. This will consist of over 13,059 pairs of twins 15 years of age and over; 9,209 pairs of the same sex and 3,850 pairs of opposite sex.